Gardenias are flowering plants that grow in USDA zones 8 through 10. The plant is kept as an ornamental shrub by gardeners because of its large, white flowers that contrast with deep green leaves. Gardenias are susceptible to many plant diseases and pests, including aphids and bacterial leaf spot. Gardenias need temperatures of 68 to 74 degrees F during the day and no lower than 60 degrees at night.
Gardenias need a high level of humidity to thrive. The required high temperatures and high humidity can make it difficult to grow gardenias indoors without a humidifier. Humidity levels are better maintained in a greenhouse than inside a home. Outdoors, gardenias should be planted in regions that are humid and warm. Misting the plants with a water sprayer will not substitute for the high humidity levels gardenias need.
The soil a gardenia is planted in should be loose and should drain well. If an area often has standing water after a rain shower, it is too wet for a gardenia. The soil should be fertilized once a month from April through November. Use an acidic fertilizer that is made for flowering plants. Use only the package's recommended amount to avoid damage to the gardenias.
Gardenias prefer partial shade outdoors, with full sun part of the day and shade the rest of the day. If the plants are being grown indoors, they require full sunlight. In the winter, keep indoor gardenias close to a window that gets southern exposure to allow it the most sunlight possible each day.
Gardenias vary in size with the climate they are grown in. All gardenias require warm, humid conditions, but the hotter the climate, the higher the plants will grow. The northernmost range of gardenia-friendly areas will grow gardenias that are about 3 feet tall. In areas closer to the Southern costs of the U.S., gardenias will grow as tall as 6 feet.
Bud drop is a problem gardenias sometimes exhibit when their moisture level isn't correct. Gardenias need to have moist soil as well as good drainage. If the flowers fall off before they bloom, the plant may be getting either too much or too little water. Keep the soil from getting dried out between waterings but to avoid bud drop, don't allow the plant to stay in standing water. The problem can also be caused by fast fluctuations in temperature, cold winds and replanting.